Anaerobic digestion is run by microbial communities that break down organic feedstock inside a sealed, oxygen-free tank, releasing biogas (mostly methane) as they grow. Their growth rate depends on how much carbon (energy/cell-building material) and nitrogen (protein-building material) the feedstock supplies relative to each other — the carbon-to-nitrogen (C:N) ratio.
blend C:N = 1 / Σ(fᵢ / CNᵢ)
fᵢ = mass fraction of feedstock i
CNᵢ = that feedstock's own C:N ratio
yield(C:N) peaks near 25:1–30:1
- Too high C:N (e.g. straw-heavy) — abundant carbon, too little nitrogen. Microbes can't build enough new biomass, so growth and digestion crawl.
- Too low C:N (e.g. food-waste-heavy) — abundant nitrogen releases excess ammonia during digestion, which becomes directly toxic to the microbial population above a threshold concentration.
- The blend sliders mix three feedstocks with distinct natural ratios — straw (high C:N), cattle manure (moderate) and food waste (low C:N) — so the operator can dial the mixture toward the 25:1–30:1 optimum that no single feedstock hits alone.
Real-world relevance: biogas plant operators co-digest manure with straw or food waste for exactly this reason — blending compensates for each feedstock's individual imbalance and keeps the digester's microbial population productive.